differences between 240 and 280 steering racks

[grannyknot]

I should know this but don't,  is there a significant difference between the 240 and 280 steering racks?  Or more to the point can a 240 steering rack be swapped into a 280 ?

Thanks

[Captain Obvious]

The bushing width on the 280 rack is wider than the 240.

There are also other differences beyond that but I don't think they would affect form-fit-function. Stuff like details in the design of the inner tie rod ends. Different, but would be unnoticeable in application. But the only form-fit-function hurdle I can come up with quickly is the bushing issue.

[grannyknot]

Thanks Captn, so the turn ratio would be the same?

[rturbo 930]

240 racks are a little quicker. 

[Captain Obvious]

9 hours ago, grannyknot said:

Thanks Captn, so the turn ratio would be the same?

Honestly, I'm not sure. It appears that way, but the specs in the manuals are all kinds of screwed up. I dug into it a bunch in this "steering effort" thread:

https://www.classiczcars.com/forums/topic/61176-steering-effort-differences-between-years/

but never completely confirmed most of the numbers. In that thread, we nailed down the lock-to-lock is different on the 240 vs. everything that came after (but just because the L-L is different does not guarantee that the ratio is different). We also nailed down that the 240 used a different pinion and rack gear than everything that came after (but just because the gear and rack are different part numbers, does not automatically require that the ratio is different).

So, I would defer to rturbo.

[Zed Head]

I'm not 100% because my brain doesn't mesh with whatever Nissan means with their newer-former-superceded interchange lingo but I think that they're saying "Yes".  Not really sure though.  They left some boxes unchecked I think.

http://www.carpartsmanual.com/datsun/Z-1969-1978/steering/steering-gear/2

[rturbo 930]

  

On 3/22/2011 at 2:33 PM, cygnusx1 said:

OK The 76 280Z rack travels roughly 1.5" per turn of the input shaft. There are 3 full turns lock to lock on the 280Z. There you have it. Pretty significant difference that can easily be felt. The 240Z is much closer to what a modern car with power steering has. The 280Z just feels "off the mark" after coming from a modern car, or a 240Z. I shall proceed with the 240Z rack swap into the 280Z.

Rough Measurements:

240Z (1972) - 1.81" of travel per 360 deg of steering.

280Z (1976) - 1.5" of travel per 360 deg of steering

https://forums.hybridz.org/topic/99017-240z-rack-into-280z/

[grannyknot]

Thank you Gents, good info.

[Namerow]

 

The Specs tables in the FSM's seem to say that the 280Z got a 15.8:1 rack for the first two years (MY 75-76) before changing back to a ratio similar to that of the 240-260 MY's (18:1 for the MY77 280Z vs. 17.8:1 for the NA-spec 240Z/260Z).  This makes no sense, for a couple of reasons:

A 15.8 rack (just like the Euro-spec 240Z) is faster but requires more driver effort than a 17.8 rack.  Not good for us slow-driving, parallel-parking North Americans.  But then the 280Z comes along and it's designed as safer and more luxurious (and heavier) than the 240Z, so as to further cater to the North American mass market.  The (numerical) steering ratio for the  280Z should have gone up, not down.  And that's exactly what the FSM spec chart says happened -- but not until MY 77 (and not by very much).  However...

If you look again in the 75 FSM, you'll see that the introductory text at the start of the 'Steering' section says that the ratio is 18:1.  That makes more sense.  I wonder if the FSM editor forgot to update the Specs table at the end of the section?  And then forgot to do it again for the 76 FSM.  

Of course, this doesn't explain the differences in rack travel measured by cygnusx1 on hybridz for his 240Z vs 280Z racks.  At 1.5" (76 280Z) vs. 1.81" (72 240Z), his measurements were definitely consistent with a slower rack in the 280Z (i.e. more wheel twirls per inch of output), but they also suggest a difference in ratios of 20%, which means that the 280Z ratio should be 17.8 x 1.2  = 20.6:1.  That's a lot more than 18:1. 

Edited March 28, 2021 by Namerow
correction to source of rack travel measurements

[rturbo 930]

For the record, those are not my measurements. 

[Namerow]

18 hours ago, rturbo 930 said:

For the record, those are not my measurements. 

Sorry about that.  I've edited my post.

[grannyknot]

@zKars, this where you step in, drawing from your vast collection and layout a steering rack from each series with definitive measurements, what say you? 😄